1. Field of the Invention
This invention relates to static structures, and more particularly to a manhole testing cover and method for its use in testing for leakage from a manhole.
2. Description of the Prior Art
Manholes form a part of a gravity sewer system. The manholes are formed from cylindrical sections of pre-formed concrete stacked one on the other from the sewer level up to ground level. The manhole allows access into the sewer. A single manhole may be anywhere from two feet to thirty feet in height and contains as many as ten individual sections. The manhole sections are presumably sealed together during construction to form a unit, and a seal is necessary to prevent ground water from seeping into the manhole, and also to prevent exfiltration from polluting the ground.
It is common for municipalities to require that the manholes be tested for leakage. The prior art manhole leakage test involves closing the main lines of the sewer by air bags, and thereafter filling the manhole with water under a head maintained two feet below the top of a manhole for a period of thirty minutes, after which period the drop in the water level is tested. If the drop in the water level exceeds, for example, a quarter of an inch, then the presumption is made that there is excess leakage from the manhole.
The use of water as a testing medium for manhole leakage has considerable disadvantages. The chief among these is that it can be remarkably difficult to locate a source of water sufficiently close to the manhole to be tested. Furthermore, following the testing of the manhole, it is necessary to pump the water back out of the manhole and dispose of it. Thus, what sounds like a very simple test to conduct under the circumstances normally encountered, becomes an expensive, time consuming and a tedious regimen.
There is therefore a need for an apparatus and a method for testing leakage from a manhole which is inexpensive to construct but accurate in results. The apparatus should also be simple to use. Lastly, the apparatus should negate the need for water as a testing medium.